1. Field of the Invention
This invention relates to organic electronic devices in which the active layer is an organic material. More particularly, it relates to electronic devices covered by flexible composite barrier structures.
2. Description of the Related Art
Organic electronic devices include devices that emit light (such as light-emitting diodes that make up displays) or respond to radiant energy (such as photodetectors). Displays may contain active matrix addressing or passive matrix-addressing. In passive matrix displays there is an array of electrode lines for addressing individual pixels arranged in rows and columns; applying a voltage between a particular row and column energizes the pixel with that corresponding address. By analogy with active matrix liquid crystal displays, the polymer electronic device (display) can be addressed at individual pixels using a thin film transistor (TFT) device which switches that pixel on and off. In such a configuration each TFT is electrically connected by to “gate busline” and to “data busline” that also need to be connected to the electrical driver circuitry and thus sealed outside the active device area.
In all such devices, an organic active layer is sandwiched between two electrical contact layers. At least one of the electrical contact layers is light-transmitting so that light can pass through the electrical contact layer. The organic active layer may generate an electric signal in response to light through the at least one light-transmitting electrical contact layer, or may emit light through the light-transmitting electrical contact layer upon application of electricity across the electrical contact layers. In the latter case, the organic active layer contains an electroluminescent material.
It is well known to use organic electroluminescent materials as the active materials in light emitting diodes. Simple organic molecules such as anthracene, thiadiazole derivatives, and coumarin derivatives are known to show electro-luminescence. Semiconductive conjugated polymers have also been used as electroluminescent materials, as has been disclosed in, for example, Friend et al, U.S. Pat. No. 5,247,190, Heeger et al., U.S. Pat. No. 5,408,109, and Nakano et al., Published European Patent Application 443 861. The organic materials can be tailored to provide emission at various wavelengths. However, they frequently are degraded by atmospheric gases, particularly oxygen and water vapor. This sensitivity can severely limit the working lifetime of the device if the materials are not properly sealed.
Typically, the device is fabricated on a glass substrate and then hermetically sealed with epoxy to another sheet of glass. In Nakamura et al, U.S. Pat. No. 5,427,858, an electroluminescent device has a protection layer of a fluorine-containing polymer which is optionally covered with a glass shield layer. In Tang, U.S. Pat. No. 5,482,896, a material such as an epoxy or hot melt adhesive is used to seal the edges of an electroluminescent device between a rigid support and a thin (25–50 micron) glass substrate. In Scozzafava et al., U.S. Pat. No. 5,073,446, an electroluminescent device including a glass substrate has an outer capping layer comprised of fused metal particles containing at least 80% indium, in order to prevent oxidation of the second electrical contact layer. However, having glass as a substrate greatly increases the fragility of the device. Moreover, devices having a glass substrates are not flexible at or below room temperature and therefore cannot be conformed to curved surfaces.
Therefore, there is a need to improve the chemical stability of layers in organic electronic devices that are sensitive to environmental elements. There is also a need to improve the durability as well as the flexibility of such devices.